I heard that GNOME is currently trying to lobby for all applications implementing CSD. One of the arguments seems to be that CSD is a must on Wayland. That’s of course not the case. Nothing in Wayland enforces CSD. Wayland itself is as ignorant about this as X11.
The situation is that GNOME Shell and Weston require CSD, but KDE Plasma and Sway do not. In fact we created a protocol (supported by GTK) that allows to negotiate with the Wayland compositor whether to use CSD or SSD.
I’m the one who drafted that protocol and I get requests about upstreaming it regularly. If I think about it, I got contacted by pretty much every toolkit about it in private – except EFL and GTK. And every time the toolkit developers tell me “this is what we want!” My answer to this is that I’m keeping out of the discussion. I’m burnt from it and are not interested in it any more.
But of course: if toolkit developers think that this is needed, don’t get fooled by GNOME asking you to implement CSD. In the same way you can ask GNOME to support server side decorations. They could do it, because they need it for XWayland anyway.
And I can totally understand you toolkit developers to not want to implement CSD. It’s a lot of work and it’s difficult to not look like an alien in the various desktop environments.